1. Field of the Invention
The invention relates to an image forming apparatus such as a printer, a copying machine, an ink jet printer, a thermal head printer, a dot impact printer, or a facsimile apparatus of the electrophotographic type or a compound apparatus of these, and particularly to a surface, surface roughness, surface smoothness, or surfaceness discriminating device for discriminating the surfaces of recording materials applicable to these.
2. Description of Related Art
Various kinds of image forming apparatuses heretofore known are generally apparatuses for forming an image on a sheet-like recording material such as plain paper, a postcard, cardboard, an envelope or a plastic thin sheet for OHP, and in an apparatus such as a printer, a copying machine or a facsimile apparatus using the electrophotographic process as a typical example thereof, a toner is used as a developer and a toner image is formed on the recording material by electrostatic image forming means, whereafter the recording material is heated and pressurized by fixing means to thereby fusion-bond the toner image on the recording material and accomplish image formation.
Also, apparatuses such as a printer, a copying machine and a facsimile apparatus using the ink jet process which are other apparatuses use ink as a developer, and form an image on a recording material by image forming means for discharging the ink at a high speed from a recording head constructed by the use of a number of nozzles having minute orifices by the utilization of mechanical or thermal reaction.
Apparatuses such as a printer, a copying machine and a facsimile apparatus using the heat transfer process use an ink ribbon as a developer, and form an image on a recording material by image forming means for thermally transferring ink from the ink ribbon by the use of a thermal head.
By the way, these apparatuses have been improved in recent years and contrivances for a higher quality of image and a higher processing speed have come to be realized by various means and at the same time, a measure for reduced costs has also been contrived and lower prices have been advanced and the apparatuses have come to spread widely.
However, the kinds of recording materials used in these image forming apparatuses are various from plain paper to high-class paper subjected to special surface treatment for use as an envelope and a resin sheet for OHP. Further, these recording materials have come to be used all over the world with the spread of the apparatuses and therefore, it has become necessary to cope with any recording materials used in various parts of the world so as to be capable of forming good images, and particularly the roughness of the surfaces of recording materials with greatly affects the image forming conditions is a very important factor.
For example, in an apparatus adopting the electrophotographic process, when the surface of the recording material used is smooth (hereinafter referred to as smooth paper) and when the surface of the recording material used is rough (hereinafter referred to as rough paper), the heating efficiency of transmitting heat from a heat source to the paper surface in a fixing portion differs in accordance with the heat resistance difference due to the difference in surface roughness, and if the rough paper is fixed at a fixing temperature proper for the smooth paper, insufficient fixing will result and therefore, for the rough paper, it is necessary to fix at a higher temperature. Thus, in the apparatuses as they are, the temperature which can fix the rough paper is used as the fixing temperature and the smooth paper remains fixed always at an excessive temperature and further, for rougher paper, a still higher fixing temperature is necessary and therefore, when such paper is used, there has been provided a selecting mode for making a user change the setting of the fixing temperature.
As a specific example of these, the basic construction of a printer adopting the electrophotographic process is shown in FIG. 3A of the accompanying drawings.
FIG. 3A is a cross-sectional view of the essential portions of a conventional printer, and in the printer, the surface of a photosensitive drum 102 is uniformly charged to a predetermined polarity by a charging roller 101, whereafter charges are eliminated from only that area of the photosensitive drum 102 which has been exposed by exposing means 103 such as a laser to thereby form a latent image on the photosensitive drum 102. The latent image is developed and visualized as toner image by the use of a toner 105 in a developing device 104. That is, the toner 105 in the developing device 104 is triboelectrically charged to the same polarity as the charged surface of the photosensitive drum 102 between a developing blade 104a and a developing sleeve 104b, and a DC bias and an AC bias are superimposed and applied in a developing gap portion wherein the photosensitive drum 102 and the developing sleeve 104b are opposed to each other, and the toner 105 is caused to selectively adhere to the latent image forming portion of the photosensitive drum 102 while being floated and vibrated by the action of an electric field, whereafter the toner 105 is carried to a transfer nip portion formed between a transferring roller 110 and the photosensitive drum 102 by the rotation of the photosensitive drum 102.
On the other hand, a recording material 107 such as paper on which an image is to be recorded has its leading edge portion fed from a recording material containing box 107xe2x80x2 to a pair of vertically conveying rollers 106xe2x80x2 by a pair of feed rollers 107xe2x80x3, and thereafter it is conveyed to a pair of ante-transfer conveying rollers 106 by the pair of vertically conveying rollers 106xe2x80x2, and is further conveyed to the transfer nip portion along a transfer guide plate 109 at a prescribed angle of entry by the ante-transfer conveying rollers 106. During the time when the recording material 107 is conveying from the ante-transfer conveying rollers 106 to the transfer nip portion, the surface of the recording material 107 may be charged by the frictional contact thereof with various members with which the recording material 107 contacts until it is conveyed to this area and therefore, a charge eliminating brush 108 for eliminating such unnecessary charges which may become a factor disturbing the image when electrostatic recording is effected is provided so as to contact with the back side of the recording material 107 being conveyed, and is grounded.
In order to electrostatically attract the toner 105 on the photosensitive drum 102 to the recording material 107 side in a transferring portion, a high voltage opposite in polarity to the toner 105 is applied to a transferring roller 110 on the back of the recording material 107, whereby the toner 105 is electrostatically attracted to the back of the recording material 107 and the toner image is transferred to the recording material 107 and also, the back side of the recording material 107 is charged to a polarity opposite to that of the toner 105, and transferring charges for continuing to hold the transferred toner 105 are imparted to the back side of the recording material 107.
Lastly, the recording material 107 to which the toner image has been transferred is conveyed to a fixing device 112 comprised of a heating rotary member 113 and a pressure roller 114 forming a nip portion therewith, and is heated and pressurized while being controlled to a constant temperature by constant temperature control means 116 provided on the heating rotary member 113 side so as to maintain a fixing temperature preset in the nip portion, whereby the toner image is fixed.
Adhering substances such as the toner differing in polarity remain slightly on the surface of the photosensitive drum 102 after the toner image has been transferred therefrom and therefore, the adhering substances on the surface of the photosensitive drum 102 after it has passed the transfer nip portion are scraped off by a cleaning blade 111a on a cleaning container 111 counter-abutting against the surface of the photosensitive drum 102, whereafter the photosensitive drum 102 stands by in preparation for the next image formation.
In the above-described steps, a fixing device of the contact heat type good in the heat efficiency and safety is widely known as an image fixing process, and use has heretofore been made chiefly of a heat roller fixing device comprised of a heat fixing roller comprising a metallic cylinder mandrel having a mold-releasable layer formed on the surface thereof, and containing a halogen heater in the cylinder, and a pressure roller comprising a metallic mandrel having an elastic layer of heat-resistant rubber formed thereon, and having a pressure side mold-releasable layer formed on the surface thereof, the pressure roller being brought into pressure contact with the heat fixing roller, but in recent years, as a type still higher in heating efficiency, use has come to be made of a film heating type fixing device as shown in FIG. 3B of the accompanying drawings which comprises a fixing film unit 113xe2x80x2 comprised of fixing film 113xe2x80x2 comprising heat-resistant resin film 113cxe2x80x2 of low heat capacity having an electrically conductive primer layer 113bxe2x80x2 formed thereon, and further having a mold-releasable layer 113axe2x80x2 formed on the surface thereof, a ceramic heater 115 inside it and a heater holder 113dxe2x80x2 serving also as a film guide member, and a metallic stay 113exe2x80x2 for uniformly pressurizing, and a pressure roller 114 comprising a pressure mandrel 114c having a silicon rubber layer 114b and a PFA tube layer 114a formed thereon, the pressure roller 114 being brought into pressure contact with the fixing film unit 113xe2x80x2.
In the ceramic heater 115 of the above-described film heating type fixing device, as shown in the cross-sectional view of FIG. 3C of the accompanying drawings, electrically energized heat generating members 115b comprising band-like patterns formed of a material such as silver palladium (Ag/Pd), RuO2 or Ta2N are formed in two rows on one surface of a ceramic substrate 115a formed of alumina or the like, and the surface thereof is covered with protective glass 115c, and a thermistor 115d as temperature detecting means is formed on the surface thereof opposite to the heat generating member forming surface.
The film heating type fixing device of this kind, from the recent viewpoint of energy-saving promotion, has drawn attention as a type high in heat transfer efficiency and quick in the rising temperature speed of the apparatus as compared with a conventional heat roller type using as a fixing roller a cylindrical metal containing a halogen heater therein, and has come to be applied also to machines of a higher speed, and particularly in this type, importance is attached to the temperature rising speed and therefore, it is necessary to make the heat capacity of the heating surface of a fixing portion small and as a result, it is difficult to form an elastic layer on the heating surface, and a hard heating surface is used. Thus, the fixing process of this kind is liable to cause a difference in the heating efficiency due to the concavo-convexity difference of the surface of the recording material.
In various image forming apparatuses such as printers using such a fixing device, with the higher processing speed as previously described, there arises the problem that the difference in fixing property becomes remarkable due to the difference in the kind of paper, and it is necessary for the user himself to input a proper fixing mode to the printer in advance in conformity with the kind of paper the user is about to use. FIG. 4 of the accompanying drawings is a flowchart showing the fixing step in the image forming process of a conventional apparatus, and here is shown an example in which two ways of selection of ordinary smooth paper and rough paper having a rough surface are made possible simply as the setting of the kinds of paper.
In the flowchart shown in FIG. 4, when rough paper is selected, fixing is effected with the temperature made higher by xcex1 relative to the fixing temperature T for ordinary paper, and the rough paper is full-power-heated at the rated power upper limit value of the heater from a point after a printing signal has been received until the fixing temperature of each mode is reached, and after a target value is reached, constant temperature control is effected until the fixing of the last paper is ended so that the heater temperature lowering in conformity with the quantity of heat taken away with the supply of paper may be maintained constant to thereby maintain the fixing temperature.
The flow of the fixing step by such a flowchart is basically the same in both of a heat roller fixing device and a film heating type fixing device, but in the latter, the temperature of the back side of a heater substrate is detected and temperature control is effected and therefore, the heating action of members, such as the pressure roller, other than the heater increases the heat accumulating effect of the entire fixing device resulting from the continuous supply of paper, and there occurs a case where the actual temperature of the fixing nip portion becomes higher than the controlled temperature of the heater (accordingly, strictly, it is not appropriate to call the controlled temperature in the fixing device of this type the fixing temperature, and hereinafter this controlled temperature will be referred to as the attempered temperature). Therefore, as a countermeasure for preventing drawbacks such as the hot offset by excessive heating (the phenomenon that the toner is too much fused and is partly residual on the fixing film side and thereafter, readheres to inappropriate locations on the paper), the backward scattering of the toner and bad paper conveyance resulting from the production of a great deal of water vapor, it is necessary to stepwisely lower the heating temperature of the heater at a predetermined rate in accordance with the number of supplied sheets, and at this time, the fixing start temperature for the rough paper is made higher than the fixing start temperature for the ordinary paper and also, the number of supplied sheets for which the temperature is to be lowered is set at a proper value individually found in conformity with the characteristic of each sheet of paper.
FIG. 5 of the accompanying drawings is a graph showing changes in the attempered temperature for each sheet and each number of supplied sheets in a conventional image forming apparatus designed to stepwisely lower the attempered temperature as described above, and by following such setting, there is realized a film heating type fixing device having a fixing speed of sixteen (16) sheets per minute.
However, compelling the user to select a mode in order to change over the fixing condition for each kind of paper used in the manner described above has caused an increase in the user""s burden of work and also has led to the possibility that when a wrong mode is selected, the fixing property for the sheets to be printed therein becomes deficient or conversely excessive heating is effected to thereby waste electric power and bad images due to high temperature offset occur and the contamination of the fixing device by the toner results.
Also, as in recent years, in an environment of use wherein a plurality of users share a network printer, it may be possible that a user uses special paper and effects mode setting changeover conforming thereto, whereafter the special paper is left in the apparatus and therefore, when another user who does not know it uses the apparatus, the mode does not coincide and appropriate fixing fails to be done, and this also leads to the high possibility of the above-noted problem arising.
Also, regarding the number of settable fixing modes, strictly there are various levels of the smoothness of actual paper and it is impossible to provide an optimum condition for each of them and therefore, sheets of paper having a certain range of smoothness are fixed together in the same mode to thereby limit the number of set modes, and there is a case where for particular paper, fixing is effected by the use of more than necessary electric power, and depending on the combination of paper and setting, there is also a case where inefficient fixing is effected.
On the other hand, in the aforedescribed apparatus adopting the ink jet process, the necessary amount of ink differs between a case where the recording material used is smooth paper and a case where the recording material used is rough paper, and even if an image is formed on rough paper with an amount of ink proper for smooth paper, the ink will permeate into the paper in the direction of thickness thereof to thereby cause the deficiency of density and therefore, for the rough paper, it is necessary to discharge more ink. Therefore, in the apparatus as it is, the amount of ink discharge for the rough paper has been used as the standard amount of discharge and for the smooth paper, images have remained formed always with excessive ink.
Also, in the apparatus adopting the thermal transferring process, the necessary amount of electric power differs between a case where the recording material used is smooth paper and a case where the recording material used is rough paper, and even if an image is thermally transferred onto the rough paper with an amount of electric power proper for the smooth paper, heat resistance is great and therefore the transferability of ink has been lowered to thereby cause the deficiency of density.
As described above, in any of the apparatuses as they are, excess temperature, ink or electric power is consumed to prevent the deterioration of the quality of image by the surface roughness of the recording material, and to prevent this, it is necessary to change over these conditions in conformity with the surface roughness of the recording material, but heretofore only such a method as compels the user to take the trouble to change the setting has been conceived.
So, in recent years, there have been made several propositions of apparatuses in which the surface roughness of a recording material is detected and image forming conditions are changed in conformity with the result of the detection to thereby effect image formation, and among them, apparatuses shown in Japanese Patent Application Laid-Open No. 2000-314618 and Japanese Patent Application Laid-Open No. 2000-356507 are mentioned as what propose the detecting principle of detecting means for the surface roughness of the recording material.
In these propositions, there is disclosed a method of detecting a physical phenomenon such as vibration or frictional sound caused by the frictional contact of contacting means for contacting with the surface of the recording material with the surface of the recording material, and detecting the difference in the amount of detection thereof as a difference in the surface roughness, and as a specific construction therefore, there is proposed a construction in which a piezoelectric element is provided on the contacting means to thereby convert vibration into an electrical signal and detect it.
In the above-described propositions, however, a specific constructional condition necessary for a member (hereinafter referred to as a probe) to be actually brought into contact with the surface of the recording material is not disclosed in detail, but there is only shown a construction in which a simple straight probe has one end thereof fixed on the downstream side in the scanning direction and has its upstream side distal end made to obliquely abut so as not to oppose the direction of movement of the recording material, and it is difficult to actually realize highly accurate detection from such content alone.
That is, as regards the difference in surface roughness between smooth paper and rough paper actually used as recording materials, when measured by a surface roughness meter usually used as a measuring device, the concavo-convexity difference of the surface of paper heretofore recognized as smooth paper is within a range of 15-20 xcexcm at maximum, and the concavo-convexity difference of the surface of paper heretofore recognized as rough paper is within a range of 22-40 xcexcm at maximum, and generally between the two, there is only a difference of about 15 xcexcm, and the difference between smooth paper approximate to rough paper and rough paper approximate to smooth paper is only of the order of several xcexcm. For the straight probe to obliquely abut against the surface of a recording material being conveyed and read such a minute concavo-convexity difference, there would occur to mind such limitations as the necessity of a very sharp needle-like shape for the tip end of the probe so as to be capable of following the concavo-convexity of several xcexcm, the necessity of wear resistance capable of withstanding the frictional contact with tens of thousands of sheets of recording material till the end of the life of the apparatus and such a degree of rigidity that the probe will not be readily deformed even if deformed paper is supplied during the occurrence of jam, the necessity of such a degree of strong abutting pressure that the tip end of the probe will not leap up even if it frictionally contacts with the recording material at the conveying speed thereof, and the necessity of such a range of light abutting pressure as can follow without flattening the concavo-convexity of the soft surface of the recording material, and it is very difficult to make these contradictory conditions compatible, and from the viewpoints of at least durability and reliability, a needle-like probe virtually cannot be used and it is unavoidable to realize highly accurate detection by a probe which is high in rigidity to some extent. For this reason, a thin-plate-like probe higher in rigidity and hard to damage the surface of the recording material is conceived as a practically usable probe, and there would occur to mind a method of scanning the surface of the recording material not by a point, but by a side having a finite length, and discriminating the kind of the recording material by the intensity difference of vibration attributable to the surface roughness averaged by this scanning width, and a construction of this kind is shown in Japanese Patent Application Laid-Open No. 2000-356507.
FIGS. 6A and 6B of the accompanying drawings show the construction of a surface roughness sensor using the thin-plate-like probe, and FIGS. 7A and 7B show the result of having actually scanned the surfaces of a plurality of recording materials differing in surface roughness by the use of the surface roughness sensor using the thin-plate-like probe.
FIG. 6A is a top plan view of the surface roughness sensor, and FIG. 6B is a cross-sectional view of the surface roughness sensor as it is seen from a side thereof in the scanning direction, and as the probe, use is made of a linear type cross section probe 117 having a T-shape when it is seen from its top surface and having a straight cross-sectional shape.
The straight type cross section probe 117 is comprised of a T-shaped metal plate 118 of a thickness 0.15 mm made of SUS and a piezoelectric element 119 adhesively secured thereonto, each of a piezoelectric element side electrode 119xe2x80x2 and a metal plate side electrode 118xe2x80x2 soldered, the T-shaped longer side portion being fixed onto a rotary support shaft 120, the distal end 117xe2x80x2 of a width 5 mm of the shorter side portion abutting against the surface of the upstream side of the recording material on the downstream side in the direction of movement of the recording material at an oblique angle of 30xc2x0, and a coil winding spring (not shown) provided on the rotary support shaft 120 so that a pressure force of 3 g-10 g can be applied to the distal end portion of the sensor with the frame of the apparatus as a fixed end.
The straight type cross section probe 117 produces distortion therein by vertical vibration created in the distal end of the metal plate by the frictional contact thereof with the paper (which strictly may be considered to be reciprocal vibration along an arcuate locus described by the distal end portion of the sensor, and if the paper conveying property is ignored and the sensor is made to abut against the scanning surface while being approximated to perpendicularity thereto, the horizontal component during vibration can be increased, but in this conventional construction, the position at which the distal end portion of the sensor can completely contact with the paper is only the initial abutting position, and after the distal end portion of the sensor frictionally contacts with the paper at that position and is jumped up, the extraneous force of a horizontal component resulting from paper conveyance become difficult to act and therefore, the vibration component in the scanning direction does not much increase even if the paper conveying property is sacrificed, and basically the vibration component in the vertical direction attributable to the concavo-convexity of the surface of the paper may be considered to be dominant) and the signal of the piezoelectric element made electromotive thereby is amplified to forty (40) times by an amplifying circuit (not shown) and is introduced into a measuring device at a period of two (2) msec. (a sampling speed which can be processed by an ordinary printer) (however, in the above-described construction, a construction using a rotary support shaft to pressurize and fix the sensor is not described in the aforedescribed example of the conventional art, but only a construction for simply fixing an anti-abutting side end portion is shown, but if the anti-abutting side end portion is completely fixed when paper is actually conveyed, there will be the possibility that it may hinder the conveyance of paper or injure the surface of the paper as long as the pressure is not set to very light pressure, and if on the other hand, the abutting pressure is too low, there will arise the problem that the paper will not be sufficiently frictionally contacted, and the contacting property of the sensor is also changed by the thickness of paper being conveyed and therefore, for the convenience of the accuracy of experiment, use is made of a rotary support shaft fixing method which is one of the constructions of the present invention).
The recording materials evaluated at this time are rough paper and smooth paper having a difference in smoothness therebetween as shown in FIG. 7A of the accompanying drawings (the letter xe2x80x9cAxe2x80x9d indicates rough paper of the bond origin, xe2x80x9cBxe2x80x9d indicates smooth paper normally used, and xe2x80x9cCxe2x80x9d indicates high-class rough paper having its surface decorated with wavy convex portions, and each number indicates the basis weight of each kind of paper), and when these recording materials were continuously conveyed at a speed of 141 mm/sec. in the named order and the sensor was made to scan them, the signal level was too low at weight of 3 g and therefore, the recording materials were pressurized with weight of 10 g, and the result thereof is shown in the graph of FIG. 7B of the accompanying drawings.
The smoothness is the number of seconds measured by a particular test apparatus for which a predetermined amount of air passes through the concavo-convexity of the surface of a sample piece. Accordingly, the less is the concavo-convexity of the surface, the smaller becomes the numerical value.
It is considered that for the paper of FIG. 7A higher in smoothness, the more difficult it is for vibration to be created in the sensor, and for the rough paper lower in smoothness, the more liable to occur is vibration in conformity with the concavo-convexity thereof and therefore, the height of the signal intensity in the graph of FIG. 7B should be in a relation converse to the height of the smoothness in FIG. 7A.
However, as can be seen from the graph of FIG. 7B, the sensor signal tends to become somewhat low for B75 or B105 which is paper particularly high in smoothness, but generally there is no signal intensity difference between smooth paper and rough paper or the relation between the two is reversed, and even if as previously described, the contact property between the sensor and the paper is improved by the use of the rotary support shaft fixing method of the present invention, it has been difficult to detect the sufficient difference in the smoothness of the paper by the sensor of such construction to thereby discriminate between smooth paper and rough paper.
Accordingly, a plurality of heating conditions and fixing conditions or image forming conditions must be provided in conformity with the kinds of paper and for the changeover of these conditions, the user must select a mode suited for the paper used in conformity with that paper, and in such an image forming apparatus, this has led to the problem that when the user has made a mistake in setting or does not know that the kind of paper has been changed in a network printer, bad images due to the deficiency of heat treatment or the deficiency of the fixing property, density or the like may result, or conversely excessive heating may waste electric power and also may cause the bad images due to high temperature offset or the toner contamination of the fixing device, or excess developer may be consumed.
Also, in a method already proposed as a solution to the above-noted problem, wherein a metal plate having a piezoelectric element is made to frictionally contact with a recording material to thereby measure the difference in the roughness of the recording material as a difference in vibration intensity, and on the basis of the result thereof, the control of the heating temperature, the fixing temperature, the image forming conditions, etc. is changed over, the difference in vibration intensity cannot be sufficiently detected simply by making the tip end of a straight type metal plate frictionally contact the surface of the recording material, and practical discrimination between smooth paper and rough paper is impossible.
It is an object of the present invention to provide a surface discriminating device which does not require the recording material selection setting by a user and well discriminates the surface of a recording material even if a recording material having any surface roughness is used, and an image forming apparatus having the same.
It is another object of the present invention to provide a surface discriminating device having a probe and a piezoelectric element provided between the first end portion and second end portion of the probe, the probe having a fixed end portion and a second end portion capable of contacting with a recording material, wherein the probe contacts with and moves relative to the recording material to thereby scan the recording material, and the surface of the recording material is discriminated by an output from the piezoelectric element during the scanning of the recording material by the probe, and the probe has a bent portion, on the second end portion side thereof, and an image forming apparatus having the same.
Further objects of the present invention will become apparent from the following description.